A gas turbine engine typically includes a compressor which compresses air and delivers the air into a combustion section. In the combustion section air is mixed with fuel and combusted. Products of this combustion pass downstream over a turbine section. In one type of gas turbine engine, there are both low pressure and high pressure compressors, and low pressure and high pressure turbines. A “coupling stack” may attach the low pressure turbine to the low pressure compressor by means of a shaft, such that the low pressure turbine drives the low pressure compressor to rotate. A tie-bolt may connect the two, and extends along a center line axis of the gas turbine engine. The coupling stack may also include a spanner nut, and a tab lock to connect the components.
During assembly, the tie-bolt may be stretched by a tool to provide a high amount of preload pressure, or tension, to the tie-bolt. When the tool is released, the tension on the tie-bolt provides compression throughout the coupling stack. The preload pressure provides enough force throughout the coupling stack to control relative movement between the components of the coupling stack. However, during operation, vibrations may cause the components to become unspooled, or loosened, such that the components may rotate relative to each other. Unspooling between components can cause a loss of preload pressure within the coupling stack.
Referring to FIGS. 2A-B, the coupling stack may also include a stack nut 100 to connect the components of the coupling stack. The stack nut 100 may be threadingly engaged with the shaft 102. A method of ensuring anti-rotation between the stack nut 100 and the shaft 102 is to deploy a key washer 104 and snap ring 106 between the stack nut 100 and the shaft 102. The key washer 104 includes a plurality of radially outer tabs 108 that are disposed within slots 110 between axial tabs 112 on the stack nut 100. The key washer 104 additionally includes radially inner tabs 114 that are disposed within slots 116 between axial tabs 118 on the shaft 102. Once the key washer 104 is installed such that the radially outer tabs 108 are disposed within the slots 110 and the radially inner tabs 114 are disposed within the slots 116, the snap ring 106 may be installed to prevent the key washer 104 from becoming disengaged from the stack nut 100 and the shaft 102. The snap ring 106 is positioned in cavities adjacent the axial tabs 112. Interference between the radially outer tabs 108 and the axial tabs 112 on the stack nut 100, as well as between the radially inner tabs 114 and the axial tabs 118 on the shaft 102, prevents relative rotation between the stack nut 100 and the shaft 102.